The present invention relates to magnetostatic wave devices comprising a layer or wafer of magnetic material exposed to an external magnetic field. When the propagation velocity of magnetostatic waves is modified within clearly defined ranges, as in optics, diopters are formed, which can partly reflect, refract or guide these waves. By means of a conductive strip traversed by a high frequency alternating current, it is possible to excite spin wave and magnetostatic wave modes in a polarized magnetic layer.
The selective excitation of magnetostatic waves makes it possible to obtain devices having a certain similarity with other known devices, such as elastic surface wave devices. However, the propagation of magnetostatic waves can be accompanied by undesirable absorption phenomena due to a possible residual coupling with the spin wave moves. On producing a magnetic wafer or layer of adequate thickness, obtainable for example by epitaxy on a non-magnetic substrate, it is possible to exchange magnetostatic waves between microstrip transducers without being disturbed by the spin wave spectrum. This procedure has given rise to magnetostatic wave devices able to operate in a wide frequency band.
In wave propogation devices, various solutions have been proposed for producing a propagation velocity change in selected regions of a substrate traversed by waves. These solutions make it possible to bring about guidance by total reflection, focusing by refraction or a simple wave reflection.
In the case of magnetostatic waves, such a wave velocity change can be obtained by hollowing out predetermined regions of the surface of the magnetic wafer or layer. The thickness reduction of the magnetic layer reduces the propagation velocity. The disadvantage of this procedure is that the thinner portions aid the excitation of spin wave modes due to interference existing in the etched areas. In order to bring about a wave velocity change, which does not give rise to the excitation of spin waves, it has been proposed to localize the regions in which this change is to take place, by metallically coating the magnetic wafer or layer. This solution leads to an increase in the propagation velocity, but has the disadvantage of introducing high transmission losses. However, it is possible to reduce the attentuating effect of a metallic coating by removing it from the magnetic layer, but this improvement necessitates a more complex production process. In order to obviate the aforementioned disadvantages, the invention proposes using ion implantation for locally reducing the magnetic properties of a magnetic medium. The absence of the hollowing out process and the elimination of a metallic coating make it possible to obtain, by reducing the effective thickness, a reduction in the propagation velocity without any excitation of spin waves and without any transmission attenuation.